1. Field of Invention
The present invention relates to a reduction-type starter for an internal combustion engine, more particularly to a starter of the reduction-type having a motor shaft, an idle shaft and a pinion drive shaft, wherein a reduction of rotation is performed in this order and at two stages and wherein an over-running clutch is provided on the idle shaft.
2. Brief Description of Prior Art
Two kinds of reduction-type starters are known in the art, that is, a reduction-type starter wherein an over-running clutch is provided on a pinion drive shaft, and a starter wherein the over-running clutch is provided on a motor shaft. In the starter, a transmitting torque applied to the clutch is a value obtained by multiplying the torque of a starter motor by a reduction ratio, while the moment of inertia of the starter motor has an influence on the clutch by the self-multiplication of the reduction ratio Accordingly, in the former conventional starter, a clutch having a large capacity is required since the torque applied to the clutch is high, resulting in a drawback that the reduction in weight can not be realized. Further, it is disadvantageous in that the outer diameter of the clutch may be inevitably increased unless the module is decreased at the sucrifice of the mechanical strength of the reduction gear, in a case that the reduction ratio is intended to be made greater for the conventional starter employing the outer ring of the clutch as the reduction gear.
In the latter conventional starter, for example, as disclosed in Japanese Examined Patent Publication No. 58-12471, according to which the over-running clutch is provided directly on the motor shaft to decrease the transmitting torque applied to the clutch and to reduce the influence on the clutch by the moment of inertia of the starter motor, the rotational speed of the starter motor is so high, above 20,000 rpm, that the conventional clutch may not be used.